Method of ramp stop detection for VCM velocity-controlled retract

Abstract

A method and apparatus for controlling the parking of a transducer head in a disk drive. A drive current is provided to a motor which controls movement of the head in a direction to move the head to a parking position. The arrival of the head at the parking position is detected. Upon this detection, a drive stop sequence is initiated to stop providing the drive current a short time after the head reaches the parking position. In one embodiment, it is determined whether the head has reached the parking position by monitoring the back emf (bemf) of the motor controlling the head, typically a voice coil motor (VCM). The detection of a sharp decline in the bemf indicates the head has stopped.

1. A method for controlling movement of a head in a disk drive comprising:
 positioning the head at any of a plurality of positions; 
 providing drive current to a motor after positioning the head; 
 detecting information indicative of a position of the head after the drive current has been provided to the motor, the motor controlling the movement of the head; and 
 generating a command that controls the movement of the head in response to the detected information. 
 
     
     
       2. The method of  claim 1  wherein detecting the information comprises monitoring a back emf of the motor and detecting a drop in the back emf indicative of a speed reduction. 
     
     
       3. The method of  claim 1  wherein detecting the information comprises detecting when a polarity of the back emf reverses. 
     
     
       4. The method of  claim 1  wherein the command initiates a drive stop sequence that comprises continuing to provide the drive current for a predetermined increment after the head has reached a predetermined position. 
     
     
       5. The method of  claim 1  wherein the command initiates a drive stop sequence, the drive stop sequence comprising:
 monitoring a back emf of the motor after the back emf crosses a zero speed threshold indicating arrival of the head at a predetermined position; and 
 detecting when a predetermined threshold is subsequently crossed. 
 
     
     
       6. The method of  claim 1  further comprising:
 controlling a velocity of the head while the drive current is provided to move the head to a predetermined position. 
 
     
     
       7. The method of  claim 6  further comprising maintaining the head within a predetermined velocity range. 
     
     
       8. A method for controlling movement of a head in a disk drive comprising:
 positioning the head at any of a plurality of positions; 
 providing drive current to a motor after positioning the head; 
 monitoring a back emf of the motor controlling the movement of the head; 
 detecting information indicative of a position of the head after the drive current has been provided to the motor based on detecting a change in the back emf; and 
 generating a command that controls the movement of the head in response to the detected information. 
 
     
     
       9. The method of  claim 8  wherein detecting the change in the back emf comprises one of detecting a drop in the back emf indicative of a speed reduction or detecting when a polarity of the back emf reverses. 
     
     
       10. The method of  claim 8  wherein the command initiates a drive stop sequence in response to the detected information, the drive stop sequence comprising one of:
 continuing to provide the drive current for a predetermined increment after the head has reached a predetermined position, or 
 monitoring a back emf of the motor after the back emf crosses a zero speed threshold indicating arrival of the head at the predetermined position, and detecting when a predetermined threshold is subsequently crossed. 
 
     
     
       11. An apparatus for controlling movement of a head in a disk drive comprising:
 a motor positioning the head at any of a plurality of positions; 
 a driver proving drive current to a motor after positioning the head; 
 a detector detecting information indicative of a position of the head after the drive current has been provided to the motor, the motor controlling the movement of the head; and 
 a controller, responsive to the information detected by the detector, that generates a command that controls the movement of the head. 
 
     
     
       12. The apparatus of  claim 11  wherein the detector comprises a back emf monitor that detects a drop in the back emf indicative of a speed reduction. 
     
     
       13. The apparatus of  claim 11  wherein the detector detects when a polarity of the back emf of the motor reverses. 
     
     
       14. The apparatus of  claim 11  wherein the command initiates a drive stop sequence that comprises continuing to provide the drive current for a predetermined increment after the head has reached a predetermined position. 
     
     
       15. The apparatus of  claim 14  wherein the controller further comprises:
 a back emf monitor to monitor a back emf of the motor after the back emf crosses a zero speed threshold indicating arrival of the head at the predetermined position; and 
 a detector to detect when a predetermined threshold is subsequently crossed. 
 
     
     
       16. The apparatus of  claim 11  further comprising:
 a velocity controller to control a velocity of the head while the drive current is provided to move the head toward a predetermined position. 
 
     
     
       17. The apparatus of  claim 16  wherein the velocity controller maintains the head within a predetermined velocity range. 
     
     
       18. An apparatus for controlling movement of a head in a disk drive comprising:
 a motor positioning the head at any of a plurality of positions; 
 a driver providing drive current to the motor after positioning the head; 
 a back emf monitor that monitors a back emf of the motor, the motor controlling the movement of the head; 
 a detector that detects information indicative of a position of the head after the drive current has been provided to the motor, the detector detecting the information based on detecting a change in the back emf; and 
 a controller, responsive to the information detected by the detector, that generates a command that controls the movement of the head. 
 
     
     
       19. The apparatus of  claim 18  wherein the detector detects the information by one of:
 a drop in the back emf indicative of a speed reduction, or 
 a polarity reversal of the back emf. 
 
     
     
       20. The apparatus of  claim 18  wherein the command initiates a drive stop sequence in response to the detected information, the drive stop sequence comprising one of
 continuing to provide the drive current for a predetermined increment after the head has reached a predetermined position, or 
 monitoring a back emf of the motor after the back emf crosses a zero speed threshold indicating arrival of the head at the predetermined position, and detecting when a predetermined threshold is subsequently crossed.